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Temperatures in the 90’s may tend to bring out the crabbiness in some of us but our vegetable gardens are basking in glory of the steamy weather. Last summer was far too cool and wet for vegetable plants to perform well but we seem to be making up for lost ground this summer. In spite of the help from Mother Nature there are things we still need to be aware this time of the growing season.
Tomato plants love the heat and some have started to set fruit while others may be on the verge of early maturity. Other things on tomatoes are growing well too. The leaf spot diseases of tomatoes have been enjoying the warm, humid weather our area has experienced for the past few weeks. Many of these leaf spot diseases can mimic each other in their early stages of development. It is important to determine what may be affecting tomato plants to make a proper diagnosis and select the most appropriate management for each disease.
EARLY BLIGHT is a fungal disease that can infect all parts of the tomato plant. The symptoms usually begin on the leaves and start out as small brown spots and eventually grow together from the bottom of the plant, up. There is usually a small yellow halo surrounding the spots. These symptoms eventually form a bull's-eye appearance and cause leaf defoliation. Fruit symptoms also include a bull's-eye, spotted appearance. These spots become large, and eventually will cause fruit drop.
LATE BLIGHT is also a fungal disease that infects quickly and development is enhanced by humid and rainy conditions. (More prevalent last year and during the fall). This disease creates brown, water soaked lesions on stems, leaves, and fruit. Management of this disease is very important.
SEPTORIA LEAF SPOT is a fungal disease of tomatoes that effects the foliage but not the fruit. In some cases the disease can be so severe that it defoliates the entire plant causing little to no fruit production. This disease produces tan spots with a dark outer ring. Spots begin at the bottom of the plant and quickly spread upward. This fungus can begin and spread from weeds so proper garden sanitation is important.
BACTERIAL SPOT (heat loving) and BACTERIAL SPECK (cool and moist loving) are two bacterial diseases of tomato are difficult to differentiate between but management is the same for both. These diseases both start as small, dark spots with yellow rings on the leaves and can cause complete leaf browning and drop. These diseases are carried by the tomato seeds and under the right conditions can quickly spread to infect the entire plant.
These diseases all share common factors in their development and control;
*All become most evident during this time of the season.
*All are generally present in tomato plantings to some degree but become a problem when conditions are beneficial for fungal development.
*All these pathogens can winter in garden soils so thoroughly cleaning leaf debris from gardens in the fall is critical.
*Properly space plants to allow for good air circulation.
*Select disease resistant varieties… some old-fashioned favorites are more susceptible to damage from disease.
*Water gardens during the morning to allow foliage to dry during the day.
*Rotate crop locations to prevent over-wintering spores from infecting new plantings.
*Keep irrigation off of foliage by applying water only to the soil surface.
*Only purchase plants from a reputable grower. Certain chain store suppliers were cited for distributing these diseases with their product within our area last season.
*Organic, copper-based fungicides are helpful in disease control. Waiting until you have a severe problem may limit the effectiveness of spraying so watch for the weather conditions that favor disease and scout your plants regularly.
I hope you are now ready to have a closer look at your tomato plants and be better able to know when and how to prevent and cure tomato leaf disease issues.
Now go outside and have fun in the dirt.